This invention relates to a sensing system in which the sensor is an optical fibre.
Usually the fibre will be a temperature sensor, but other variables such as pressure or stress may also be sensed.
Several forms of temperature sensors based on optical fibres are already known. In Applied Optics, Vol. 20, No. 19 1st Oct. 1981, pages 3408 to 3414, M. Gottlieb and G. B. Brandt describe a fibre optic temperature sensor in which thermally generated black-body radiation produced by a hot spot within the core of the fibre itself is sensed. In the same journal and volume, No. 22, 15th Nov. 1981, pages 3867 to 3873, the same authors describe an optical fibre temperature sensor in which transmission intensity effects are sensed; the device relies on loss effects in the cladding and jacket of the fibre.
A disadvantage of both prior art arrangements is that temperature can be sensed only at one position, at which the maximum temperature occurs, and that that position is unknown.